Currently, heat-dissipating fans commonly used in personal computers include an axial-flow fan, a centrifugal fan and a cross-flow fan. Of these, the most popular one is supposed to be an axial-flow fan.
Referring to FIG. 1, a conventional axial-flow fan is primarily consisted of a rotor device 10 and a frame 11 arranged beside the rotor device for supporting the rotor device. The frame 11 includes a motor holder (not shown) and a plurality of ribs 13 arranged between the outer frame 11 and the motor holder. The rotor device 10 includes a motor (not shown) received on the motor holder and a plurality of rotor blades 12 to work on the surrounding air to generate an airflow. Through the work of the rotor blades on the surrounding air, the blast pressure is changed from a relatively low value on the air inlet side into a relatively high value on the air outlet side. That is, there is a blast pressure enhancement on the air outlet side.
Unfortunately, when the airflow flows through the fan having the structure as shown in FIG. 1 and as described above, turbulent flows will be generated after the airflow encounters the ribs so as to have an adverse effect on the blast pressure enhancement. Consequently, the efficiency of the fan is reduced.
In addition, in order to avoid the interruption of operation due to the breakdown of fan used in the heat-generating system, a set of standby fan is usually provided and connected with the original fan in series to prevent the heat-generating system or device from being damaged. Moreover, because the total pressure of the axial-flow fan is relatively low, the axial-flow fan cannot fully develop a high airflow rate in a system of a high resistance. Thus, in the case that a high total pressure is needed, two or more axial-flow fans are connected in series to provide the high total pressure.
Typically, a so-called serial fan is constituted by two independent fan units assembled through a specific circuit design. Each fan unit respectively includes a frame and a rotor device. After these two fan units are assembled respectively, both of them are coupled together through screws (not shown), thereby completing the construction of the serial fan. However, the serial connection of two fan units can not guarantee that the total pressure of the airflow discharged from the fans can be doubled. In other words, even though one fan unit rotates and the other is used as a standby fan, the latter will also decrease the blast pressure discharged from the rotating fan because both of them will be interfered with each other while connected in series, thereby significantly decreasing the overall heat-dissipating efficiency or even generating a lot of noise.
Therefore, it is desirable to develop a heat-dissipating system which can effectively eliminate the interference between the fans assembled together, provide a supercharging function, and reduce the noise generated when the fans are operated.